Impacts of glyphosate-based herbicide on leaf stomatal density and biomass production of transgenic soybean (Glycine max [L.] Merr.) and corn (Zea mays L.)

The application of glyphosate-based herbicides (GBH) for weed management can influence crop physiology, such as stomata-dependant processes (ex. stomatal conductance, transpiration and water use efficiency). However, no information exists about the relationship between GBH and stomatal development. The objective of this study was to assess the impact of GBH applications on stomatal density in glyphosate-resistant crop cultivars. It was conducted in randomized agricultural plots cultivated with Roundup Ready soybean (Pioneer P10T91R(R)) and corn (Pioneer P9675AMXT(R)). The treated crops were exposed to one or two Roundup540(R) applications, at a rate of 1.67 L ha(-1), at different vegetative growth stages (V2 and R1 in soybean; V2 and V4 in corn). Stomatal densities (StoDen) and plant's biomass were measured at different growth stages for corn (V2, V4 and R2) and for soybean (V2, R1 and R4). We observed that single GBH applications on soybean plants were associated with higher StoDen and dry weight. Also, the soybean leaves collected in the control plots were associated with significantly lower values of StoDen, dry weight at R4 stage. Little differences between the treatments were observed in corn plants but treated leaves had higher stomatal densities. Influence of GBH on crop plants vary between adaxial (upper) and abaxial (lower) surface and growth stage. The results suggest that soybean is more sensitive than corn to GBH applications, which resulted in an obvious change in the development of the stomata after each GBH application. This change on StoDen seems to have a positive influence on the biomass production of plants exposed to GBH compare to the control plants. However, this positive influence is less striking while doubling the applied quantity of GBH.